Vitamin B12 release through bacteriophage-mediated cell lysis of the marine bacterium Sulfitobacter sp. M39.

Vitamin B₁₂ (B₁₂) is an essential cofactor for vital metabolic processes in both prokaryotes and eukaryotes. De novo B₁₂ biosynthesis is exclusively carried out by a modicum of prokaryotes, although being required by most organisms. Recently, it has been demonstrated that not all B₁₂-prototrophic bacteria voluntarily share this vital cofactor and, therefore, are termed B₁₂-retainers. Consequently, low biosynthesis potential and limited voluntary release lead to a large discrepancy between availability and demand for B₁₂ in the ocean, indicating that release of B₁₂ may be an important control. Hence, in this study, we examined a specific release process, cell lysis after phage infection. We isolated bacteriophages specific for the B₁₂-prototrophic, yet B₁₂-retainer bacterium Sulfitobacter sp. M39. The addition of the bacteriophages to a Sulfitobacter sp. M39 mono-culture led to a significant increase in virus-like particles, reduced bacterial growth, and quantifiable extracellular dissolved B₁₂. When introducing bacteriophages to a co-culture comprising the host bacterium and the B₁₂-auxotrophic diatom Thalassiosira pseudonana, we observed rapid response in the form of microalgal growth. Our results indicate that B₁₂ is released as a result of bacteriophage-mediated cell lysis of Sulfitobacter sp. M39, enabling the growth of T. pseudonana in co-culture and possibly other microbes in nature. Therefore, we propose that bacteriophage-mediated cell lysis is a key mechanism for the release of essential metabolites, including vitamins, and given the estimated bacteriophage infection rates in the ocean, it plays a crucial role in the B-vitamin cycle in the marine environment.